$ B = \left[\begin{array}{rrr}0 & 2 & 1 \\ 2 & 1 & 1 \\ 1 & 1 & 2\end{array}\right]$ What is $ B^{-1}$ ?
$ = \left[\begin{array}{rrr}-\frac{1}{5} & \frac{3}{5} & -\frac{1}{5} \\ \frac{3}{5} & \frac{1}{5} & -\frac{2}{5} \\ -\frac{1}{5} & -\frac{2}{5} & \frac{4}{5}\end{array}\right]$